Check the contacts in those sockets. If they don't hold the bulbs, it sounds like they are not completely intact. Also, on your misfire... (I have a 4.6) plugs and wires first. If it hasn't been done in a long time, have a mechanic familiar with these do the job. They know all the tricks, especially if a plug gets stuck, or wire gets fused to the plug well wall. You can also isolate fuel injectors yourself as the cause easily. Idle the engine and remove and replace one injector connector plug at time. If the idle does not drop when you remove the plug then that injector could be bad. Also it's a good idea to go to the auto parts store and pick up some extra wire looms. Believe it or not, plug wire routing is an issue with high-power coil packs like ours (another reason COP units were developed). The wires can cross fire and induce other circuits, so look at any wire-over-wire crossings that are close to each other or near other things (i.e. fuel injectors because they have coils in them). If anyone reading has owned a Bronco then they know that crossing (I think it was...) wires 7&8 guaranteed a misfire, even with new 8mm wires. So bottom line on that is check your wire routing for things like this and where a wire may sit on something very hot, etc. Use a scan tool to find where the ECU thinks the misfire is coming from. That will help narrow it down. Lastly, on the hvac problem... you might have a vacuum leak (this can also cause misfires and other issues). The quickest and easiest way to detect that is to find a mechanic with a smoke machine. They seal off the throttle body and inject smoke (like dance floor smoke) into the intake. The smoke comes out where it's leaking. You would be amazed what that finds. On mine, it found a break in the PVC hose in an area where it was covered with insulation, so there was no hiss and nothing visible, but once fixed... what a difference! Just PM me if you need any info/help.

 

Happen to know about this specific procedure? Is it best to use all motorcraft parts?

To remind you its the 1998 Expedition XLT 4.6 L SOHC. I'm getting conflicting information from mechanic friends is why I ask. Everyone I ask who works on cars thinks they do it, but I'm highly skeptical because 2 of you have told me it is a specific procedure. Also saw something about only using motorcraft parts (or autolite which is made by Ford?), but others say that using the cheaper versions of plugs and wires would be fine.The going rate for labor seems to be about 100-140. Since you seem to know your stuff, whats your input on this? Or anyone else?

Thanks

 

Perhaps "procedure" wasn't the correct word to use, "precautions" is better suited.

1. Before removing spark plugs the plug wells need to be blown (or vacuumed) out to prevent any debris from falling into the cylinders.

2. Loosen the spark plugs a 1/4 to 1/2 turn, spray a bunch of penetrating oil down the well, then work the plugs back and forth before attempting to remove them.

3. Apply anti-seize to the threads of the new spark plugs.

4. Install the new plugs and torque them to EXACTLY 13 ft. lbs., no more, no less.

 

Aluminum heads is why you need to use the precautions. Just treat it like an outboard engine for a boat. As far as plugs, I've been told and scolded for using non-platinum plugs. I guess you want to be changing these as infrequently as possible, so platinum seems to be the way to go. Be really careful around plug #4. It's definitely the worst out of all of them. Standing in front, facing the engine, 1-4 is on your left, front to back. 5-8 is on your right, front to back. I used Autolite. YMMV. I would recommend investing in some wire labels to identify them and some more looms to keep them from flopping around. Watch the ones that leave the driver's side coil pack and run near the fan and over the water pump. They can contact the fan if not properly routed and secured. When you're done, bacitracin and band-aids, and then it's beer and buffalo wing time. :-)

 

That plus the earlier heads only had 3 threads in the spark plug holes. Later years it was upped to 5 threads because of the spark plugs blowing out issue.